Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Continued snowfall and wind-drifting are creating dangerous avalanche conditions. Triggering a 1-2 foot thick avalanche is likely in steep, wind-loaded terrain. While unlikely, we can't rule out the possibility of triggering a very large, 3-4 foot thick avalanche—especially on very steep, rocky, wind-affected slopes. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    The Sawtooths and western Smoky Mountains picked up 3-7" of snow since yesterday morning. Snow will continue today, adding an additional 2-4". Wind blew moderate yesterday from the W, likely building small wind slabs in exposed terrain. This problem will be most widespread at upper elevations with greater snow amounts that are exposed to stronger wind. 

    Wind speeds will be light for a good portion of today but will increase this afternoon. Remember that fresh slabs can form in a surprisingly short amount of time. Look for active wind-loading and cracking in the snow surface. Small wind slab avalanches (see video to right/above) can be great triggers for more deeply buried weak layers. Any avalanche that steps down to these persistent weak layers will be large and destructive.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    "Weak snow near the ground" is the mantra of the winter. Two months ago, we buried a widespread, thick layer of facets. This layer has been responsible for the vast majority of the avalanche activity we've seen since. Unfortunately, it's shown few signs of improvement. 

    However, one factor that's helping our cause is its burial depth. As this layer becomes more deeply buried it becomes harder to impact. In the Sawtooths, you'll find this layer under a stout 3-4' thick slab of snow. What we're left with is a low-probability but high-consequence avalanche problem. Your odds of triggering an avalanche on this layer are low, but the resulting slide would be massive. 

    These avalanches are most likely in very steep, rocky, wind-affected terrain where "trigger points" exist. Trigger points are locations where the overlying slab is thinner and the weight of you and-or your sled can more easily impact the weak layer. 

    ADDITIONAL DISCUSSION:Recent storms produced many natural and human-triggered avalanches on a layer of facets and surface hoar, now buried 1-2' deep. Recent observations indicate that this layer has gained strength. However, I wouldn't discount it just yet, particularly where it presents as a standing stripe of surface hoar. 

    (2/9/2021) Crown and debris from a large natural avalanche on McDonald Peak in the southern Sawtooths. This slide occurred sometime overnight on Sunday, during the ongoing wind event that loaded many slopes with stiff, dense slabs, and scoured many others. Visible are textures that indicate scouring (in the upper left) and loading (in the bottom right).

Avalanche Discussion

Snowfall has returned to the northern and western portions of the forecast area as a series of Pacific storms impact the region through tomorrow. You can see our updated storm table here, or check out your favorite weather station here. Snowfall amounts are modest so far, with 3-7" in the mountains around Banner, the Sawtooths, and the western Smokys. An additional 2-4" is expected in these areas today as well as another 6-8" tonight through tomorrow. 

All said and done, we're looking at 10-20" of new snow by Saturday afternoon. This amount of snow and some wind is plenty enough to create avalanche problems on its own. Yesterday, Ben could hear the wind at upper elevations around Banner Summit and observers noted moderate to strong wind along the high peaks of the Smokys. Although we'll see a little lull in the wind today, it's forecast to increase as the next shot of snow arrives this afternoon. 

What, if anything, this amount of snow and wind-loading does to our buried weak layers is uncertain. Recent observations of the facet and surface hoar layer buried in late January are showing signs of improvement. The last likely collapse associated with this layer was one Ben experienced in the Fishhook drainage of the Sawtooths on Monday. Even still, I think we're better assuming this added snowfall may wake things up until proven otherwise. Where and if we see activity on existing persistent weak layers will give us great information moving forward.

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